A hydraulic vehicle brake system with an anti-skid system and a control device is known from U.S. Pat. No. 4,809,183. Furthermore, a hydraulic pressure source and at least one evaluating circuit are associated with the anti-skid system for detecting an oversteering tendency, an understeering tendency and the start of the danger of skidding, and for generating control signals for the anti-skid system, so that this system automatically brakes at least one wheel of the vehicle with the use of the hydraulic pressure source. The automatic braking stabilizes the vehicle, thus counteracting an oversteering tendency, an understeering tendency, or a danger of skidding, or skidding that is already in progress. The pressure source is not shown. To obtain the control signals, king pin inclinations are measured, for example, and compared with preselected threshold values. The rotating velocity of the vehicle around the vertical axis can also be observed by means of a gyroscope, for example. Alternatively, transverse accelerations can be measured by means of acceleration sensors associated with the axles and evaluated.
German Patent Disclosure DE 41 09 925 A1 discloses a hydraulic vehicle brake system with two advantageous, closed brake circuits and an anti-skid system that operates in accordance with the so-called recirculating pump principle, and in which a combination of a controllable 2/2-way valve and a cylinder with a separating piston and a restoring spring for the separating piston is installed for each brake circuit, between this anti-skid system and a main brake cylinder, to control the cornering of a vehicle; a common auxiliary pump and a 3/2-way valve disposed downstream of it are also provided for both brake circuits for controlled charging of the separating piston and to control the 2/2-way valves, which are hydraulically controllable by means of control inputs for closing the brake lines of the brake circuits between the cylinders and the main brake cylinder. Pressures generated in the cylinders after the main brake lines have been blocked are modulated by means of the anti-skid system and supplied individually to the wheel brakes of the four wheels. The anti-skid system can also individually reduce the pressures supplied to the wheel brakes. A control device that controls both the 3/2-way valve and the anti-skid system to improve the cornering of the vehicle equipped in this manner can also activate a driving motor for the auxiliary pump. The disadvantage is that, because of the hydraulic connection of the cylinders with modulation valve arrangements of the anti-skid system, the auxiliary pump must deliver a pressure at the level of the highest brake pressure to be expected during cornering. Correspondingly, the auxiliary pump must be embodied to be powerful; a required driving motor is heavy and stresses an electrical system of the vehicle in a disadvantageous manner. The heavy driving motor and the heavy auxiliary pump are expensive. A further disadvantage is that, because of the high pressure generated, disturbing and possibly very aggravating noises occur during pump operation. A reservoir that can be charged by the auxiliary pump is also expensive, as is the electrically controllable 3/2-way valve that controls the charging of the separating piston and the hydraulic control inputs of the 2/2-way valves. Moreover, because of the embodiment of the cylinder and its separating piston, the respective 2/2-way valve must be combined with a check valve function, so that during automatic brake operation the transition into normal brake operation can immediately take place solely through operation of the brake pedal. Therefore, in the disclosed exemplary embodiment the symbol of a check valve is allocated to the second position of the 2/2-way valves.
German Patent Application P 42 32 311.8 (DE 42 32 311 A1) proposes to embody a hydraulic vehicle brake system equipped with an anti-skid device that operates in accordance with the recirculating-pump principle and designed for automatic braking for the purpose of improving the driving performance of a vehicle during cornering, for example, and/or traction control at powered wheels, by means of the arrangement of pistons and cylinders and 2/2-way valves and an auxiliary pressure source for automatic braking such that, during automatic brake operation, the least possible noise is emitted from the auxiliary pressure source and the anti-skid device, and little driving energy is required. This is achieved in accordance with the proposal in that the auxiliary pressure source is embodied as a low-pressure source for charging the pistons, and that the cylinders supply intakes of recirculating pumps with a pressure medium, via controllable 2/2-way magnet valves, only when brake pressure is to be generated or increased in one of the respective wheel brakes downstream of the recirculating pumps. It can be considered disadvantageous that two separating pistons, of which each has its own associated brake circuit, respectively have their own cylinder that must be sealed tightly by means of a lid. Moreover, the one auxiliary pump used to hydraulically charge the two separating pistons is to be hydraulically connected to both cylinders.